Method and system for searching cascading failure accident chain of new energy high-proportion power grid

Abstract

The invention discloses a new energy high-proportion power grid cascading failure accident chain searching method and system. The method comprises the steps of obtaining parameters of all new energy units and current collection lines in a new energy station; establishing an equivalent model of the new energy station; constructing an anticipated fault set, performing time domain simulation on power grid operation modes under different faults, calculating voltage safety risk indexes of the power grid under different faults, and screening typical faults; performing time domain simulation on the power grid operation mode under the typical fault, and calculating the off-network probability and moment of the new energy unit; selecting an off-network object; performing time domain simulation on the operation mode of the power grid again until the power grid loses stability or the number of chain reaction cascade faults reaches a threshold value, and recording a cascading fault accident chain of this time; time domain simulation is carried out on power grid operation modes under all typical faults one by one, and statistics is carried out to form all possible cascading fault accident chains. The problems of poor practicability and low efficiency when a current cascading failure analysis method is applied to a new energy high-proportion power grid are solved.

Description

Technical Field

[0001] This invention belongs to the field of power system cascading failure analysis, specifically relating to a method and system for searching accident chains of cascading failures in power grids with a high proportion of new energy sources. Background Technology

[0002] The cascading failure mechanism and evolution law of power grids with a high proportion of renewable energy differ significantly from those of traditional AC power grids. The strong random fluctuations, low disturbance immunity, and weak support capabilities of renewable energy generation, as well as the decline in grid inertia and transient voltage support capabilities brought about by the large-scale integration of renewable energy, greatly increase the risk of cascading failures in the power grid, posing a severe challenge to the safe operation of the power grid.

[0003] Currently, most research on cascading failures focuses on traditional AC systems, with relatively little research on the mechanisms and evolution paths of cascading failures in power grids with a high proportion of renewable energy sources. Furthermore, current research on cascading failure mechanisms mainly employs complex network analysis and model analysis methods. Complex network analysis abstracts the power grid into a complex network to study the factors influencing network structure stability; however, it can only be used to analyze the impact of power grid topology and characteristic parameters on power grid security, and is difficult to apply to practical cascading failure simulation studies of actual power grids. Model analysis uses various methods such as abstraction, simplification, order reduction, and statistics to establish multiple models, thereby analyzing the mechanisms and behavioral characteristics of power network cascading failures. However, it is highly dependent on the accuracy of the modeling and struggles to analyze the impact of network topology on cascading failures, resulting in low efficiency in analyzing the evolution paths of cascading failures. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method and system for searching cascading fault chains in power grids with a high proportion of renewable energy, which solves the problems of poor practicality and low efficiency of current cascading fault analysis methods when applied to power grids with a high proportion of renewable energy.

[0005] Technical solution: The present invention provides a method for searching a chain of cascading faults in a power grid with a high proportion of new energy sources, comprising:

[0006] Obtain the parameters of all new energy generating units and power collection lines in the new energy power station; group all new energy generating units according to power, with the number of groups being C; aggregate the parameters of the new energy generating units in each group; and establish an equivalent model of the new energy power station containing C equivalent new energy generating units based on the aggregation results.

[0007] Obtain the specific operating mode of the power grid, construct a set of anticipated faults based on the specific operating mode of the power grid, perform time-domain simulation of the power grid operating mode under different faults in the set of anticipated faults, calculate the voltage safety risk index of the power grid under different faults based on the time-domain simulation results, and screen out typical faults based on the voltage safety risk index;

[0008] Time-domain simulation of power grid operation under typical fault conditions is performed to calculate the grid disconnection probability and disconnection time of each equivalent unit in the equivalent model of new energy power plants; the new energy equivalent unit that meets the grid disconnection probability threshold and has the earliest grid disconnection time is selected as the grid disconnection target.

[0009] Based on typical faults and selected disconnected objects, the time-domain simulation of the power grid operation mode is performed again. The previous step is repeated until the power grid loses stability or the number of cascading faults reaches the threshold. The simulation is then stopped, and the cascading fault accident chain is recorded.

[0010] Time-domain simulations were performed on all typical fault conditions, and all possible cascading fault chains were formed by combining the statistics of this cascading fault accident chain.

[0011] Furthermore, obtaining the parameters of all new energy generating units and power collection lines within the new energy power station includes:

[0012] Obtain the active power P of all new energy units in the new energy power station i Reactive power Q i Grid connection point voltage The rated power P of the unit N The unit's wind speed-power curve or solar radiation-power curve, and the power P at the starting point of the maximum power tracking zone in the power curve. div1 The power P at the end of the maximum power tracking zone div2 The actual high-voltage ride-off curve of the new energy source for the unit F h (t) and low voltage ride-off curve F l (t), collector line length and unit impedance, voltage at the grid connection point of the new energy power station.

[0013] Furthermore, the process involves grouping all new energy generating units by power output, with C groups, aggregating the parameters of the new energy generating units within each group, and establishing an equivalent model for a new energy power station containing C equivalent new energy generating units based on the aggregation results. This includes:

[0014] Based on the power P at the starting point of the maximum power tracking region div1 The power P at the end of the maximum power tracking region div2 All new energy generating units within the new energy power station are grouped, with the power range being [0, P]. div1 They are divided into a group with a power range of [P]. div1 ,P div2 They are divided into a group with a power range of [P]. div2 ,P N They are divided into three groups in total;

[0015] For the active power P of all new energy units in each groupi Reactive power Q i and grid connection point voltage By aggregating the power, the equivalent active power P of the new energy equivalent generating unit is obtained. eq Equivalent reactive power Q eq Equivalent voltage vector value The calculation method is as follows:

[0016]

[0017] In the formula, n C This represents the number of new energy generating units in the current group.

[0018] The equivalent impedance expression in the equivalent model of a new energy power station is as follows:

[0019]

[0020] In the formula, X is the reactance of the equivalent impedance; R is the resistance of the equivalent impedance; U represents the equivalent voltage vector value of a renewable energy equivalent generating unit. eq Re represents the equivalent voltage amplitude; Re() is used to find the real part of the vector; Im() is used to find the imaginary part of the vector.

[0021] Furthermore, the set of anticipated faults includes single-circuit three-phase short-circuit faults, single-phase permanent faults, three-phase fault-free disconnections, single-phase short-circuit trips and fault-free trips on parallel double-circuit lines on the same pole, DC commutation failures, and DC blocking faults.

[0022] Furthermore, the calculation method for the voltage security risk index of the power grid under different fault conditions is as follows:

[0023]

[0024] In the formula, I TVS V0 is the initial value of the bus voltage, representing a voltage safety risk indicator. min V represents the minimum bus voltage after the fault is cleared. th The safe threshold for voltage; T th When the voltage drops below V after the fault occurs th Tolerable time; T mx,span When the bus voltage drops below V after a fault occurs th Maximum duration; T cut The fault clearing time; The voltage average value for the last time period in the time-domain simulation; T end This represents the total duration of the time-domain simulation.

[0025] Furthermore, the time-domain simulation of the power grid operation mode under typical faults, calculating the disconnection probability and disconnection time of each equivalent unit in the equivalent model of the new energy power station, includes:

[0026] National standards require high-voltage ride-through curves (G) for new energy sources. h (t) and low voltage ride-through curve G l The region enclosed by (t) is region A, and G l (t) and the actual equipment low voltage ride-through curve F l The region enclosed by (t) is region B, and F l (t) and the region enclosed by the grid connection point voltage 0pu are region C, G h (t) and the actual equipment high voltage ride-through curve F h (t) The area enclosed is zone D, and the remaining area is zone E. After the fault occurs, the voltage V at the grid connection point of the new energy equivalent unit... u The probability of disconnection is 0 for area A, 1 for areas C and E, and P for area B. off-B The calculation method is as follows:

[0027]

[0028] In the formula, For F l The inverse function of (t); t0, t end V u The start and end times;

[0029] The probability of D area disconnecting from the network, P off-D The calculation method is as follows:

[0030]

[0031] In the formula, For F h The inverse function of (t).

[0032] Furthermore, the time-domain simulation of the power grid operation mode under typical fault conditions, and the calculation of the grid disconnection probability and disconnection time of the new energy units, include:

[0033] Calculate the disconnection times for regions B and D with non-zero disconnection probabilities, where the disconnection time T for region B is... off-B The calculation method is as follows:

[0034] T off-B =P max t l +t0

[0035] In the formula, P max This is the threshold for the probability of disconnection from the network;

[0036] D area offline time Toff-D The calculation method is as follows:

[0037] T off-D =P max t h +t0.

[0038] Furthermore, the time-domain simulation of the power grid operation mode is re-performed based on typical faults and selected disconnected objects. This process is repeated until the power grid loses stability or the number of cascading faults reaches a threshold, at which point the simulation stops. The cascading fault accident chain is recorded, including:

[0039] When any electrical quantity of the power grid, such as voltage, frequency, or power angle, fails to meet the power grid stability criteria, the power grid is considered to have lost stability. Cascading faults include high and low voltage ride-through of new energy sources, new energy source disconnection from the grid, line short-circuit faults, line disconnection, power flow transfer, DC commutation failure, DC blocking, and generator and load shedding.

[0040] Furthermore, the expression for the cascading failure chain is as follows:

[0041] ST i ={ST i,1 ,…,ST i,j ,…,ST i,m}

[0042] In the formula, ST i For a chain of cascading failures; ST i,j Let j be the event in the i-th incident chain.

[0043] Based on the same inventive concept, the present invention provides a search system for a chain reaction of power grid failures in areas with a high proportion of new energy sources, comprising:

[0044] The equivalent model building module is used to obtain the parameters of all new energy units and collection lines in the new energy power station; all new energy units are grouped by power, with the number of groups being C; the parameters of the new energy units in each group are aggregated; and an equivalent model of the new energy power station containing C new energy equivalent units is built based on the aggregation results.

[0045] The typical fault screening module is used to obtain specific operating modes of the power grid, construct a set of anticipated faults based on the specific operating modes of the power grid, perform time-domain simulation of the power grid operating modes under different faults in the set of anticipated faults, calculate the voltage safety risk index of the power grid under different faults based on the time-domain simulation results, and screen out typical faults based on the voltage safety risk index.

[0046] The module for determining the grid disconnection target is used to perform time-domain simulation of the power grid operation mode under typical faults, calculate the grid disconnection probability and disconnection time of each equivalent unit in the equivalent model of the new energy power station, and select the new energy equivalent unit that meets the grid disconnection probability threshold and has the earliest grid disconnection time as the grid disconnection target.

[0047] The cascading failure accident chain search module is used to re-simulate the power grid operation mode based on typical faults and selected disconnected objects. The previous step is repeated until the power grid loses stability or the number of cascading failures reaches the threshold, at which point the simulation stops and the current cascading failure accident chain is recorded.

[0048] The cascading fault accident chain search module is also used to perform time-domain simulations of the power grid operation modes under all typical faults, and to form all possible cascading fault accident chains by combining the statistics of this cascading fault accident chain.

[0049] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are as follows: (1) By collecting the operating condition data of the new energy unit units and the topology data and information in the station, and by using a reasonable clustering algorithm, an equivalent model of the new energy station considering the operating condition distribution characteristics of the unit units in the station is established, which improves the accuracy of the equivalent model of the new energy station; (2) By constructing a set of anticipated faults, typical faults of the new energy high-proportion power grid are screened based on the voltage safety risk index of the power grid, and a new energy disconnection probability index is established, which improves the search efficiency of the power grid cascading fault evolution path; (3) Based on the simulation data of the typical operation mode of the power grid, the typical fault screening method and the expert experience of actual production personnel are integrated, and the simulation search of the typical evolution path is carried out through time-domain simulation. The proposed cascading fault accident chain search method has strong practicality. Attached Figure Description

[0050] Figure 1 This is a flowchart illustrating a method for searching a chain of cascading faults in a power grid with a high proportion of new energy sources, as disclosed in an embodiment of the present invention.

[0051] Figure 2 This is a power curve diagram of a new energy unit disclosed in an embodiment of the present invention;

[0052] Figure 3 This is a schematic diagram of an equivalent model of a new energy power station disclosed in an embodiment of the present invention;

[0053] Figure 4 This is a low-voltage ride-through curve diagram of the national standard requirements for new energy generating units and the actual equipment, as disclosed in an embodiment of the present invention.

[0054] Figure 5 This is a power grid frequency curve diagram when a cascading fault accident chain ST1 occurs, as disclosed in an embodiment of the present invention.

[0055] Figure 6 This is a schematic diagram of a chain failure accident chain ST1 disclosed in an embodiment of the present invention;

[0056] Figure 7 This is a power grid voltage curve diagram when a cascading fault accident chain ST2 occurs, as disclosed in an embodiment of the present invention.

[0057] Figure 8 This is a schematic diagram of a chain failure accident chain ST2 disclosed in an embodiment of the present invention;

[0058] Figure 9 This is a schematic diagram of the structure of a search system for a power grid cascading fault accident chain with a high proportion of new energy sources, as disclosed in an embodiment of the present invention. Detailed Implementation

[0059] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0060] Example 1

[0061] like Figure 1 As shown, the present invention provides a method for searching a chain of cascading faults in a power grid with a high proportion of new energy sources, characterized by comprising:

[0062] S1. Obtain the parameters of all new energy units and power collection lines in the new energy power station; group all new energy units according to power, with the number of groups being C; aggregate the parameters of the new energy units in each group; and establish an equivalent model of the new energy power station containing C equivalent new energy units based on the aggregation results.

[0063] All renewable energy generating units are grouped by power output, assuming there are 3 groups. The parameters of the renewable energy generating units in each group are aggregated to obtain 3 equivalent renewable energy generating units. Then, the equivalent impedance corresponding to these 3 equivalent renewable energy generating units is calculated, forming a series of equivalent values. Figure 3 The equivalent model of the new energy power station is shown.

[0064] The specific implementation process of step S1 is as follows:

[0065] S1.1 Obtain the parameters of all new energy generating units and power collection lines within the new energy power station. Details are as follows:

[0066] Taking a certain renewable energy power station as an example, obtain the active power P of all renewable energy units in the renewable energy power station. i Reactive power Q i Grid connection point voltage The rated power P of the unit N The unit's wind speed-power curve or solar radiation-power curve, and the power P at the starting point of the maximum power point tracking (MPPT) region in the power curve. div1 The power P at the end of the MPPT region div2The actual high-voltage ride-off curve of the new energy source for the unit F h (t) and low voltage ride-off curve F l (t), collector line length and unit impedance, voltage at the grid connection point of the new energy power station.

[0067] S1.2. All new energy generating units are grouped according to their power output, with the number of groups being C, as detailed below:

[0068] Based on the power P at the starting point of the maximum power tracking region div1 The power P at the end of the maximum power tracking region div2 All new energy generating units within the new energy power station are grouped, with the power range being [0, P]. div1 They are divided into a group with a power range of [P]. div1 ,P div2 They are divided into a group with a power range of [P]. div2 ,P N They are divided into three groups.

[0069] S1.3. Aggregate the parameters of the new energy units in each group, as follows:

[0070] For the active power P of all new energy units in each group i Reactive power Q i and grid connection point voltage By aggregating the power, the equivalent active power P of the new energy equivalent generating unit is obtained. eq Equivalent reactive power Q eq Equivalent voltage vector value The calculation method is as follows:

[0071]

[0072] In the formula, n C This represents the number of new energy generating units in the current group.

[0073] S1.4. Based on the aggregation results, establish an equivalent model for a new energy power station containing C equivalent new energy generating units, such as... Figure 3 As shown.

[0074] In this embodiment, the equivalent impedance expression in the equivalent model of the new energy power station is as follows:

[0075]

[0076] In the formula, X is the reactance of the equivalent impedance; R is the resistance of the equivalent impedance; U represents the equivalent voltage vector value of a renewable energy equivalent generating unit. eqRe represents the equivalent voltage amplitude; Re() is used to find the real part of the vector; Im() is used to find the imaginary part of the vector.

[0077] S2. Obtain the specific operating mode of the power grid, construct a set of anticipated faults based on the specific operating mode of the power grid, perform time-domain simulation of the power grid operating mode under different faults in the set of anticipated faults, calculate the voltage safety risk index of the power grid under different faults based on the time-domain simulation results, and screen out typical faults based on the voltage safety risk index.

[0078] Among them, obtaining specific power grid operating modes includes, in addition to typical power grid operating modes, predicting the power situation of source, grid and load by combining expert experience rules or theoretical methods based on operating domain, confidence interval and other methods, and generating several typical power flow modes.

[0079] The set of anticipated faults includes, but is not limited to, single-circuit three-phase short-circuit faults, single-phase permanent faults, three-phase fault-free disconnections, single-phase short-circuit trips and fault-free trips on parallel double-circuit lines on the same pole, DC commutation failures, and DC blocking faults.

[0080] In this embodiment, the voltage safety risk index of the power grid under different fault conditions is calculated as follows:

[0081]

[0082] In the formula, I TVS V0 is the initial value of the bus voltage, representing a voltage safety risk indicator. min V represents the minimum bus voltage after the fault is cleared. th The safe threshold for voltage; T th When the voltage drops below V after the fault occurs th Tolerable time; T mx,span When the bus voltage drops below V after a fault occurs th Maximum duration; T cut This is the time when the fault is cleared. The voltage average value for the last time period in the time-domain simulation; T end This represents the total duration of the time-domain simulation.

[0083] Based on voltage safety risk index I TVS The criteria with an index greater than 2 are selected as typical faults. If none of them are met, the one with the largest index is selected as the typical fault.

[0084] S3. Perform time-domain simulation of the power grid operation mode under typical faults, calculate the grid disconnection probability and disconnection time of new energy units; select the new energy units that meet the grid disconnection probability threshold and have the earliest grid disconnection time as the grid disconnection targets.

[0085] The specific implementation process of step S3 is as follows:

[0086] S3.1. Perform time-domain simulation of the power grid operation under typical fault conditions to calculate the disconnection probability of new energy generating units. Details are as follows:

[0087] like Figure 4 As shown, the national standard requires that the high-voltage ride-through curve G of new energy sources... h (t) and low voltage ride-through curve G l The region enclosed by (t) is region A, and G l (t) and the actual equipment low voltage ride-through curve F l The region enclosed by (t) is region B, and F l (t) and the region enclosed by the grid connection point voltage 0pu are region C, G h (t) and the actual equipment high voltage ride-through curve F h (t) The area enclosed is zone D, and the remaining area is zone E. After the fault occurs, the voltage V at the grid connection point of the new energy equivalent unit... u The probability of disconnection is 0 for area A, 1 for areas C and E, and P for area B. off-B The calculation method is as follows:

[0088]

[0089] In the formula, For F l The inverse function of (t); t0, t end V u The start and end times.

[0090] The probability of D area disconnecting from the network, P off-D The calculation method is as follows:

[0091]

[0092] In the formula, For F h The inverse function of (t).

[0093] S3.2 Calculate the disconnection times for regions B and D with non-zero disconnection probabilities, where,

[0094] Area B offline time T off-B The calculation method is as follows:

[0095] T off-B =P max t l +t0

[0096] In the formula, P max The threshold for the probability of disconnection is usually selected from 0 to 1.

[0097] D area offline time T off-D The calculation method is as follows:

[0098] T off-D =P max t h +t0.

[0099] S3.3 Select the new energy generating units that meet the grid disconnection probability threshold and have the earliest grid disconnection time as the grid disconnection targets.

[0100] S4. Based on typical faults and selected disconnected objects, perform time-domain simulation of the power grid operation mode again, repeat step S3, and stop the simulation when the power grid loses stability or the number of cascading faults reaches the threshold, and record the cascading fault accident chain.

[0101] Among them, when any electrical quantity of the power grid voltage, frequency, or power angle fails to meet the power grid stability criterion, the power grid is considered to have lost stability. The cascading faults include, but are not limited to, high and low voltage ride-through of new energy sources, new energy source disconnection from the grid, line short circuit faults, line disconnection, power flow transfer, DC commutation failure, DC blocking, and generator and load shedding.

[0102] In this embodiment, the expression for the cascading failure chain is as follows:

[0103] ST i ={ST i,1 ,…,ST i,j ,…,ST i,m}

[0104] In the formula, ST i For a chain of cascading failures; ST i,j Let j be the event in the i-th incident chain.

[0105] S5. Perform time-domain simulations of the power grid operation modes under all typical faults, and combine the statistics of this cascading fault accident chain to form all possible cascading fault accident chains.

[0106] The equivalent and typical fault screening method for renewable energy power plants adopted in this invention provides a model and fault condition basis for time-domain simulation of cascading faults. The proposed method for calculating the probability of renewable energy disconnection from the grid provides a key technology for searching typical evolution paths of cascading faults. This invention can solve the technical problem of the difficulty in effectively searching for typical evolution paths of cascading faults in power grids with a high proportion of renewable energy.

[0107] This invention proposes a time-domain simulation search framework for cascading fault accident chains, which consists of three main steps: equivalent analysis of new energy power plants considering the operating condition distribution characteristics of on-site generating units, typical fault screening based on grid voltage safety risk indicators, and assessment of the probability of new energy grid disconnection considering high and low voltage ride-through characteristics. This framework provides guidance and key methods for searching typical evolution paths of cascading faults in power grids with a high proportion of new energy.

[0108] The following simulation examples verify the search method for the grid cascading fault accident chain with a high proportion of new energy sources in this invention.

[0109] Taking a typical operating mode of a real power grid as an example, detailed parameters of a certain renewable energy power station are obtained, where the power of the renewable energy units is shown in the table below:

[0110] Table 1 - Initial Power of Units in New Energy Power Stations

[0111]

[0112] Active power was grouped, and new energy units were divided into three groups: C1 to C3. Among them, {W3, W5, W9, W...} 10} is a C1 group; {W1,W2,W4,W6,W7,W8,W 11 W 12 W 13 W 14} is a C2 group; {W 15 W 16 W 17 W 18 This is group C3. The equivalent power and equivalent impedance of the equivalent new energy unit are calculated as shown in the table below:

[0113] Table 2 - Power and Connection Impedance of New Energy Equivalent Machine

[0114]

[0115] Construct a set of anticipated faults and calculate the power grid voltage safety risk index I under different fault conditions. TVS By comparison, DC commutation failure and N-2 faults in some lines were selected as typical faults;

[0116] Time-domain simulations were performed on selected typical faults. When commutation failure occurs in the DC system, the grid voltage drops, and the renewable energy enters low-voltage ride-through. Subsequently, a large amount of reactive power from the DC system's filter is fed back to the AC system, which is superimposed on the reactive power that the renewable energy could not back off during the low-voltage ride-through, resulting in a transient overvoltage phenomenon. The renewable energy then enters high-voltage ride-through. The probability of the renewable energy unit disconnecting from the grid at this time is calculated as shown in the table below:

[0117] Table 3 - Grid Disconnection Probability of New Energy Units

[0118] New Energy Unit Name Off-network Probability New Energy Unit Name Off-network Probability Equivalent Unit 1 0.526 Equivalent Unit 8 0.596 Equivalent Unit 2 0.547 Equivalent Unit 9 0.843 Equivalent Unit 3 0.775 Equivalent Unit 10 0.774 Equivalent Unit 4 1 Equivalent Unit 11 0.626 Equivalent Unit 5 0.741 Equivalent Unit 12 0.67 Equivalent Unit 6 0.8 Equivalent Unit 13 0.985 Equivalent Unit 7 0.758 Equivalent Unit 14 0.726

[0119] Taking the probability threshold of new energy grid disconnection as 0.7, a total of 9 new energy equivalent generators disconnected from the grid. At this time, the grid frequency dropped significantly, and the time-domain simulation curve is as follows. Figure 5 As shown. The complete chain of failures ST1 is as follows: Figure 6 As shown.

[0120] When an N-2 fault occurs on the line, the grid voltage drops, and the renewable energy units enter a low-voltage ride-through phase. The probability of the renewable energy units disconnecting from the grid at this time is calculated as shown in the table below:

[0121] Table 4 - Grid disconnection probability of new energy units

[0122] New Energy Unit Name Off-network Probability New Energy Unit Name Off-network Probability Equivalent Unit 1 1 Equivalent Unit 8 1 Equivalent Unit 2 1 Equivalent Unit 9 0.700 Equivalent Unit 3 1 Equivalent Unit 10 1 Equivalent Unit 4 1 Equivalent Unit 11 1 Equivalent Unit 5 1 Equivalent Unit 12 1 Equivalent Unit 6 1 Equivalent Unit 13 0.389 Equivalent Unit 7 0.228 Equivalent Unit 14 0.214

[0123] With a new energy source disconnection probability threshold of 0.7, a total of 11 new energy equivalent generators disconnected from the grid, causing the grid voltage to further decrease and become unstable. The time-domain simulation curve is shown below. Figure 7 As shown, the complete chain of failures ST2 is as follows: Figure 8 As shown.

[0124] Example 2

[0125] like Figure 9 As shown, the present invention provides a search system for a chain reaction of power grid failures with a high proportion of new energy sources, comprising:

[0126] The equivalent model building module is used to obtain the parameters of all new energy units and collection lines in the new energy power station; all new energy units are grouped by power, with the number of groups being C; the parameters of the new energy units in each group are aggregated; and an equivalent model of the new energy power station containing C new energy equivalent units is built based on the aggregation results.

[0127] The typical fault screening module is used to obtain specific operating modes of the power grid, construct a set of anticipated faults based on the specific operating modes of the power grid, perform time-domain simulation of the power grid operating modes under different faults in the set of anticipated faults, calculate the voltage safety risk index of the power grid under different faults based on the time-domain simulation results, and screen out typical faults based on the voltage safety risk index.

[0128] The module for determining the grid disconnection target is used to perform time-domain simulation of the power grid operation mode under typical faults, calculate the grid disconnection probability and disconnection time of each equivalent unit in the equivalent model of the new energy power station, and select the new energy equivalent unit that meets the grid disconnection probability threshold and has the earliest grid disconnection time as the grid disconnection target.

[0129] The cascading failure accident chain search module is used to re-simulate the power grid operation mode based on typical faults and selected disconnected objects. The previous step is repeated until the power grid loses stability or the number of cascading failures reaches the threshold, at which point the simulation stops and the current cascading failure accident chain is recorded.

[0130] The cascading fault accident chain search module is also used to perform time-domain simulations of the power grid operation modes under all typical faults, and to form all possible cascading fault accident chains by combining the statistics of this cascading fault accident chain.

[0131] In one optional implementation, the search method for cascading fault accident chains in power grids with a high proportion of renewable energy includes: a) obtaining parameters of all renewable energy units and collection lines within renewable energy power plants; establishing an equivalent model of the renewable energy power plants; b) constructing a set of anticipated faults, performing time-domain simulations of the power grid operation modes under different faults in the set of anticipated faults, calculating the voltage safety risk index of the power grid under different faults, and screening out typical faults; c) performing time-domain simulations of the power grid operation modes under typical faults, calculating the probability and timing of grid disconnection of renewable energy units; selecting disconnection targets; d) performing time-domain simulations of the power grid operation modes again based on typical faults and selected disconnection targets, repeating the previous step until the power grid loses stability or the number of cascading faults reaches a threshold, stopping the simulation, and recording this cascading fault accident chain; e) performing time-domain simulations of the power grid operation modes under all typical faults one by one, and statistically forming all possible cascading fault accident chains.

Claims

1. A method for searching a chain of cascading faults in a power grid with a high proportion of new energy sources, characterized in that, include: Obtain the parameters of all new energy generating units and power collection lines in the new energy power station; group all new energy generating units according to power, with the number of groups being C; aggregate the parameters of the new energy generating units in each group; and establish an equivalent model of the new energy power station containing C equivalent new energy generating units based on the aggregation results. Obtain the specific operating mode of the power grid, construct a set of anticipated faults based on the specific operating mode of the power grid, perform time-domain simulation of the power grid operating mode under different faults in the set of anticipated faults, calculate the voltage safety risk index of the power grid under different faults based on the time-domain simulation results, and screen out typical faults based on the voltage safety risk index; Time-domain simulation of power grid operation under typical fault conditions is performed to calculate the grid disconnection probability and disconnection time of each equivalent unit in the equivalent model of new energy power plants; the new energy equivalent unit that meets the grid disconnection probability threshold and has the earliest grid disconnection time is selected as the grid disconnection target. Based on typical faults and selected disconnected objects, the time-domain simulation of the power grid operation mode is performed again. The previous step is repeated until the power grid loses stability or the number of cascading faults reaches the threshold. The simulation is then stopped, and the cascading fault accident chain is recorded. Time-domain simulations were performed on all typical fault conditions, and all possible cascading fault chains were formed by combining the statistics of this cascading fault accident chain.

2. The method for searching the chain of cascading faults in a power grid with a high proportion of new energy sources according to claim 1, characterized in that, The acquisition of parameters for all new energy generating units and power collection lines within the new energy power station includes: Obtain the active power P of all new energy units in the new energy power station i Reactive power Q i Grid connection point voltage The rated power P of the unit N The unit's wind speed-power curve or solar radiation-power curve, and the power P at the starting point of the maximum power tracking zone in the power curve. div1 The power P at the end of the maximum power tracking zone div2 The actual high-voltage ride-off curve of the new energy source for the unit F h (t) and low voltage ride-off curve F l (t), collector line length and unit impedance, voltage at the grid connection point of the new energy power station.

3. The method for searching the chain of cascading faults in a power grid with a high proportion of new energy sources according to claim 2, characterized in that, The process involves grouping all new energy generating units by power output, with C groups forming the group number. Parameters of the new energy generating units within each group are then aggregated. Based on the aggregation results, an equivalent model of the new energy power station containing C equivalent new energy generating units is established, including: Based on the power P at the starting point of the maximum power tracking region div1 The power P at the end of the maximum power tracking region div2 All new energy generating units within the new energy power station are grouped, with the power range being [0, P]. div1 They are divided into a group with a power range of [P]. div1 ,P div2 They are divided into a group with a power range of [P]. div2 ,P N They are divided into three groups in total; For the active power P of all new energy units in each group i Reactive power Q i and grid connection point voltage By aggregating the power, the equivalent active power P of the new energy equivalent generating unit is obtained. eq Equivalent reactive power Q eq Equivalent voltage vector value The calculation method is as follows: In the formula, n C This represents the number of new energy generating units in the current group. The equivalent impedance expression in the equivalent model of a new energy power station is as follows: In the formula, X is the reactance of the equivalent impedance; R is the resistance of the equivalent impedance; U represents the equivalent voltage vector value of a renewable energy equivalent generating unit. eq Re represents the equivalent voltage amplitude; Re() is used to find the real part of the vector; Im() is used to find the imaginary part of the vector.

4. The method for searching the chain of cascading faults in a power grid with a high proportion of new energy sources according to claim 1, characterized in that, The set of anticipated faults includes single-circuit three-phase short-circuit faults, single-phase permanent faults, three-phase fault-free disconnections, single-phase short-circuit trips and fault-free trips on parallel double-circuit lines on the same pole, DC commutation failures, and DC blocking faults.

5. The method for searching the chain of cascading faults in a power grid with a high proportion of new energy sources according to claim 1, characterized in that, The calculation methods for the voltage security risk indicators of the power grid under different fault conditions are as follows: In the formula, I TVS V0 is the initial value of the bus voltage, representing a voltage safety risk indicator. min V represents the minimum bus voltage after the fault is cleared. th The safe threshold for voltage; T th When the voltage drops below V after the fault occurs th Tolerable time; T mx,span When the bus voltage drops below V after a fault occurs th Maximum duration; T cut The fault clearing time; The voltage average value for the last time period in the time-domain simulation; T end This represents the total duration of the time-domain simulation.

6. The method for searching the chain of cascading faults in a power grid with a high proportion of new energy sources according to claim 1, characterized in that, The time-domain simulation of power grid operation under typical fault conditions, calculating the grid disconnection probability and disconnection time of each equivalent generating unit in the equivalent model of new energy power plants, includes: National standards require high-voltage ride-through curves (G) for new energy sources. h (t) and low voltage ride-through curve G l The region enclosed by (t) is region A, and G l (t) and the actual equipment low voltage ride-through curve F l The region enclosed by (t) is region B, and F l (t) and the region enclosed by the grid connection point voltage 0pu are region C, G h (t) and the actual equipment high voltage ride-through curve F h (t) The area enclosed is zone D, and the remaining area is zone E. After the fault occurs, the voltage V at the grid connection point of the new energy equivalent unit... u The probability of disconnection is 0 for area A, 1 for areas C and E, and P for area B. off-B The calculation method is as follows: In the formula, F l -1 For F l The inverse function of (t); t0, t end V u The start and end times; The probability of D area disconnecting from the network, P off-D The calculation method is as follows: In the formula, For F h The inverse function of (t).

7. The method for searching the chain of cascading faults in a power grid with a high proportion of new energy sources according to claim 6, characterized in that, The time-domain simulation of power grid operation under typical fault conditions, calculating the grid disconnection probability and disconnection time of new energy units, includes: Calculate the disconnection times for regions B and D with non-zero disconnection probabilities, where the disconnection time T for region B is... off-B The calculation method is as follows: T off-B =P max t l +t0 In the formula, P max This is the threshold for the probability of disconnection from the network; D area offline time T off-D The calculation method is as follows: T off-D =P max t h +t0。 8. The method for searching the chain of cascading faults in a power grid with a high proportion of new energy sources according to claim 1, characterized in that, The time-domain simulation of the power grid operation mode is re-performed based on typical faults and selected disconnected objects. This process is repeated until the power grid loses stability or the number of cascading faults reaches a threshold. The simulation is then stopped, and the cascading fault accident chain is recorded, including: When any electrical quantity of the power grid, such as voltage, frequency, or power angle, fails to meet the power grid stability criteria, the power grid is considered to have lost stability. Cascading faults include high and low voltage ride-through of new energy sources, new energy source disconnection from the grid, line short-circuit faults, line disconnection, power flow transfer, DC commutation failure, DC blocking, and generator and load shedding.

9. The method for searching the chain of cascading faults in a power grid with a high proportion of new energy sources according to claim 1, characterized in that, The expression for the cascading failure chain is as follows: ST i ={ST i,1 ,…,ST i,j ,…,ST i,m } In the formula, ST i For a chain of cascading failures; ST i,j Let j be the event in the i-th incident chain.

10. A search system for cascading fault chains in power grids with a high proportion of new energy sources, characterized in that, include: The equivalent model building module is used to obtain the parameters of all new energy units and collection lines in the new energy power station; all new energy units are grouped by power, with the number of groups being C; the parameters of the new energy units in each group are aggregated; and an equivalent model of the new energy power station containing C new energy equivalent units is built based on the aggregation results. The typical fault screening module is used to obtain specific operating modes of the power grid, construct a set of anticipated faults based on the specific operating modes of the power grid, perform time-domain simulation of the power grid operating modes under different faults in the set of anticipated faults, calculate the voltage safety risk index of the power grid under different faults based on the time-domain simulation results, and screen out typical faults based on the voltage safety risk index. The module for determining the grid disconnection target is used to perform time-domain simulation of the power grid operation mode under typical faults, calculate the grid disconnection probability and disconnection time of each equivalent unit in the equivalent model of the new energy power station, and select the new energy equivalent unit that meets the grid disconnection probability threshold and has the earliest grid disconnection time as the grid disconnection target. The cascading failure accident chain search module is used to re-simulate the power grid operation mode based on typical faults and selected disconnected objects. The previous step is repeated until the power grid loses stability or the number of cascading failures reaches the threshold, at which point the simulation stops and the current cascading failure accident chain is recorded. The cascading fault accident chain search module is also used to perform time-domain simulations of the power grid operation modes under all typical faults, and to form all possible cascading fault accident chains by combining the statistics of this cascading fault accident chain.

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